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Alert Notice 418: Request for monitoring of V842 Cen in support of HST Observations

March 12, 2010: Further to AAVSO Alert Notice 417, the AAVSO requests intensive monitoring observations of the cataclysmic variable V842 Cen beginning immediately (2010 March 12.5 UT; JD 2455268.0) and continuing through 2010 March 19 (2455274.5). These observations are in support of the Hubble Space Telescope Cosmic Origins Spectrograph observations of V842 Cen planned for 2010 March 18 UT. Space Telescope ground controllers will need to know that V842 Cen is fainter than V=15 on March 17, based upon data from the night of March 16, in order to proceed with the planned observations. Observers are asked to observe V842 Cen during the next week and report their observations promptly to the AAVSO using WebObs. Please contact Dr. Matthew Templeton at matthewt@aavso.org to report your observations if it is not possible for you to use WebObs, or if you have not been assigned an AAVSO observer code. We request that intensive observations continue until at least 2010 March 19 UT before returning to a normal schedule of observations of this star.

Note that the comparison stars currently in VSP do not cover the star in its current quiescent state. All observers -- but particularly visual observers -- should note that there is a red star with V band magnitude of approximately 14.9 about 7 arcseconds south-southwest of V842 Cen, and another red star of comparable brightness about 20 arcseconds south-southwest of the variable. These objects are currently being evaluated for suitability as formal comparison stars, but for now they may be used as references for "fainter-than" estimates. Please be certain that you do not confuse the star 7 arcseconds away with the variable, and if the two are severely blended, please be sure to note this in your observation.

The NOMAD1 ID, position, and magnitudes for the two potential comparison objects are:

7": 0323-0709135 , RA 14 35 52.170 , Dec -57 37 43.82 , V=14.88

20": 0323-0709110 , RA 14 35 51.839 , Dec -57 37 57.54 , V=14.76

If using either of these objects as "fainter-than" reference stars, please give the NOMAD ID in the Comparison star name field. Note that we may update the comparison star sequence, and will be sending out a follow-up Special Notice on or before March 16.